U.S. Pat. No. 3,962,543 by Blauert et. al discloses a single user system to locate a mono sound input at a predetermined location in space. The Blauert et. al. specification applies to individual monophonic sound signals only and does not include any reverberation response and hence, although it may be possible to locate a sound at a radial position, due to the lack of reverberation response, no sound field is provided and no perception of distance of a sound object is possible. Further, it is doubtful that the Blauert et. al. disclosure could be adapted to a multi-user environment and in any event does not disclose the utilisation of sound field signals in a multi-user environment but rather one or more monophonic sound signals only.
U.S. Pat. No. 5,596,644 by Abel et al. describes a way of presenting a 3D sound to a listener by using a discrete set of filters with pre-mixing or post-mixing of the filter inputs or outputs so as to achieve arbitrary location of sounds around a listener. The patent relies on a break-down of the Head Related Transfer Functions (HRTFs) of a typical listener, into a number of main components (using the well known technique of Principal Component Analysis). Any single sound event may be made to appear to come from any direction by filtering it through these component filters and then summing the filters together, with the weighing of each filter being varied to provide an overall summed response that approximates the desired HRTF. Abel et. al. does not allow for the input to be represented as a soundfield with full spatial information pre-encoded (rather than as a collection of single, dry, sources) and to manipulate the mixing of the filters before or after the filters to simulate headtracking. Neither of these benefits are obtained by the Abel et. al.
Thus, there is a general need for a simple system for the creation of an audio environment for multiple users wherein it is designed to give each user an illusion of sound (or sounds) located in space.